Flexible material webs are used in many sectors of industrial processing. The material webs can be in the form of textile sheet-like structures, such as woven fabrics, knitted fabrics and nonwovens, or in the form of paper products, natural products, plastic products or metal products, laminar bonding materials or composites made therefrom. Foamed and/or coated and/or fibrous products are also used as flexible material webs, which are processed further subsequently.
Since material webs are usually too narrow to be wound on rollers, the material web is deposited in a zigzag form in receiving containers or at depositing points such as platforms or the like in several layers, wherein substantially more running meters of material can be accommodated than if the material is wound up on rollers.
The method of the zigzag deposition of the material web has been disclosed, for example, in the U.S. Pat. No. 5,087,140 under the name “Festooning” and the associated apparatus has been disclosed under the name “Festooner”. Here, the material web is deposited by means of a folding unit on a platform, which moves back and forth in transverse direction. The folding unit is formed by a laying arm, which is swiveled forwards and backwards in the longitudinal direction.
DE 196 44 383 C1 likewise discloses a swivel arm as a folding unit. The material web can be transported over the width of the swivel arm while the latter moves. Here, the material web is guided to the depositing point between conveyor belts circulating around rollers.
U.S. Pat. No. 3,735,554 discloses an apparatus for laying strip material, wherein the folding units disposed above cardboard boxes are arranged on a frame that can be displaced longitudinally. The folding units merely comprise two rollers. The material exiting between the rollers of the folding unit moves freely and in an unguided manner in the space above the cardboard boxes. This movement of the material is disadvantageous with respect to achieving a precise deposition of the material.
Additional types of folding units relate to rollers, as disclosed in DE 101 25 452 C2 and DE 91 16 502 U1. The laying rollers described in these patent specifications are components of a laying carriage, which can be displaced in reversible orientation. The material web is transported between the laying rollers to the depositing point. The material web is displaced together with the laying rollers or the carriage over a defined depositing length, which corresponds, for example, to the width of a pallet.
Although all these folding units disclosed in the prior art are naturally functional, problems occur when the wind caused by the movement of the material web and/or the folding unit interferes with the depositing method, particularly in the case of material webs having a low weight. In precise terms, it is possible that the material web does not reach the edge of the depositing point and is then not grasped by a hold-down device or a gripper. While on the one hand, the space at the depositing point is not used in an optimum manner, there can be a formation of wrinkles on the other hand and thus an impaired depositing behavior and depositing pattern. Another disadvantage is that the speed of the movements has to be relatively low so as to be able to deposit particularly material webs having a low weight. The higher the speed of the material web and/or the folding unit, the stronger is the air turbulence, which in turn results in position inaccuracies of the material web. The air influences are manifold and different in nature.
The disadvantageous process of depositing the material web will become particularly clear using the example of a swivel arm at the time of the change in orientation. The material web exits from the swivel arm and while it moves downwards towards the depositing point, the swivel arm swivels and causes an air resistance to a certain extent, wherein the depositing process in the boundary region of the depositing point is interrupted and the material web section intended to remain there is restrained increasingly in direct proportion to the lightness of the material web and can no longer be grasped by a hold-down device or a gripper. The process described for a swivel arm also basically applies to a laying carriage having laying rollers.
Another difficulty is with respect to the electrostatic effects, which exist on the one hand between the conveyor belt of the swivel arm and the material web, and on the other hand between the hold-down device and the material web mostly due to the plastic portions in the material. On the one hand, the exiting material web is gravitated towards the conveyor belt; while on the other hand, the already deposited material web is gravitated towards the hold-down device. Particularly lightweight material webs are subject to the forces of attraction. This results in problems during the deposition of the material web. Similar effects are also known to occur when depositing the material web using laying rollers.
The apparatuses disclosed in the prior art for depositing a flexible material web are thus capable of subsequent improvement, particularly with respect to the deposition of a material web having low weight and at high speed.
Based on the prior art, it is the object of the present invention to specify a method and an apparatus of the kind in question, wherein higher production speeds are achieved with good fold quality even in the case of material webs having a low weight.